Can your eye colour change?

Andi Horvath

Andi Horvath explores the reality about iris colour, and why it sometimes changes.

A commonly held belief among Europeans is that all babies are born with blue eyes, which can then change colour. However if one spends some time in a maternity ward meeting babies from other cultures it becomes evident that not all eyes start off blue. So what is the biology behind eye colour? For the past 15 years Professor David Mackey, an Associate Professor with the Centre for Eye Research Australia at the University of Melbourne, has been interested in the genetics of eye colour as a model for researching the genetics of eye disease.

“The iris is the aperture that controls the level of light entering the eye,” Professor Mackey explains.

“Interestingly eye colour correlates with the geographic latitude of where one’s ancestors lived. One theory suggests that eye colour in humans evolved in a similar way to skin and hair colour and is related to ultra violet (UV) radiation absorption and vitamin D production.

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“The lower level of UV light in Northern Europe meant individuals with less melanin pigment production in their hair, skin, and eyes had better absorption of vitamin D, which provided a survival advantage.

“Early humans living in lower latitudes where UV light intensity is high benefited from the protective barrier darker hair, skin and eyes provided.”

So can eye colour change without the use of spooky cosmetic contact lenses?

“People with European ancestry will tell you some of their children’s eye colour changed during their first year of life. The reason for this is that eye colour changes in these babies as melanin deposited in the iris is incomplete at birth and develops as they grow.

“However there are some disease states and conditions – such as infections and trauma – that can cause eye colour to change. Horner’s Syndrome is a condition in which the nervous system to the eye is disrupted. If this occurs at birth, the affected eye stays blue while the other eye (if genetically destined to be brown, hazel or green) becomes pigmented. Colours can appear different depending upon surrounding colours and light quality.”

So is there an official colour chart to classify iris eye colour? Several have been proposed. One of the first people to try to classify eye colour was Oscar Wild’s father, who was a noted eye and ear surgeon who had many illegitimate children. Perhaps he was looking for evidence of paternity in their eyes.

“Our Australian research group contributed to the world classification schema we use today,” Professor Mackey says.

“Colour, scientifically, is a combination of hue, saturation and brightness. We presented a nine-category grading system, which is a refined blue-green-brown spectrum. The amount of melanin, its positioning within the iris, and the structure of the iris can influence a wide range of colours.

“There are many genes that influence eye colour but the main ones can also cause albinism, in which a person makes no pigment if the gene function is completely missing at one step in the pathway. In albinism a person (or animal like a rabbit or mouse) has pink eyes.

“A system of classifying eye colour has been of interest to forensic scientists. It may soon be possible to say what colour eyes a victim or suspect had based on DNA evidence. We are not 100 per cent accurate yet as more modifier genes remain to be discovered.

“Eye colour genetics has shown to be an important research model for studying the genetics of other diseases. We can measure the genetic variation in the general population in which mild changes in the gene cause slight changes in a measure, such as eye colour, while a severe change or complete absence of the same gene causes a disease such as albinism.

“This same strategy has now worked for measures of the pressure in the eye (which helped identify genes for glaucoma), the length of the eye (which helped identify genes for short sightedness), and the thickness of the wall of the eye (which helped identify genes for the eye disease keratoconus).”

Professor David Mackey is the executive director of the Lions Eye Institute, Centre for Ophthalmology and Visual Science at the University of Western Australia, while remaining a visiting associate at the Centre for Eye Research Australia at the University of Melbourne.

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